A powered hammer may include a piston driven by a motor in a reciprocating motion and a ram in a guide channel that is driven in a reciprocating motion by an air cushion between a front surface of the piston and a rear surface of the ram. A front surface of the ram may impact a tool bit being held by a tool holder to effectuate a hammering action. This driving mechanism generates impacts on the rear end of the tool bit by reciprocating movement of the ram. In some embodiments, a beat piece may be interposed between the tool bit and the ram. In this hammering operation, the air pressure between the piston surface facing the ram and the rear surface of the ram increases, so that the ram hits directly on the rear end of the tool bit or it hits on the beatpiece which transmits the impact of the ram to the tool bit.
After having caused the forward movement of the ram the piston starts a rearward movement and, due to the recoil generated by the impact, the ram also moves backward. The ram may include an outer circumferential surface with a vent channel that extends axially from the front end of the outer surface to the rear end of the outer surface. The ram may also include an outwardly projecting O-ring disposed between the front and rear ends, interrupting a portion of the vent channel. The guide channel may include a recess defined in its wall. After the ram impacts the tool bit and recoils, the space between the ram and the piston may be temporarily connected to atmosphere through the vent channel and the recess in the wall of the guide tube. Thereby a possible loss of air in this space is compensated so that upon continued backward movement of the ram and the following forward movement of the piston an increase in air pressure in this space sufficient to cause an effective impact can be generated.
Manufacturing of the ram can be somewhat costly, as the manufacturing requires two, separate machining steps. First, a blank is machined in a machine tool that rotates the blank with respect to a machining tool bit, e.g. on a lathe, to form the outer circumferential surface. Next, after completing the first step, the axial vent channel is machined in the outer circumferential surface of the ram in another, separate machine tool.